Structural unit with x-shaped inserts

ABSTRACT

AN IMPROVED INTEGRAL STRUCTURAL UNIT HAVING TOP AND BOTTOM SURFACE MEMBERS, SPACED APART BY LONGITUDINALLY EXTENDING, WEB MEMBERS FORMING HOLLOW SPACES DEFINED BY THE TOP, BOTTOM AND ADJACENT WEB MEMBERS, SAID SPACES CONTAINING A MULTIPLICITY OF SPACED-APART STRENGTHENING RIGID INSERTS. THE IMPROVED UNIT MAY BE DETACHABLY INTERLOCKED WITH OTHER SIMILAR UNITS TO FORM A RELATIVELY FLAT STRUCTURAL SURFACE PARTICULARY SUITABLE FOR HIGH IMPACT USES SUCH AS TEMPORARY AIRCRAFT LANDING STRIPS AND AERIAL DELIVERY PLATFORMS.

Jan. 26, 1971 "K. F.BRAEUNINGER E 3,557,512

I STRUCTURAL UNIT WITH X-SHAPED INSERTS Filed Ju 1y 22, 19 68 a Sheets-Sheet 1 Q .7 Y INVENTORS.

5 I Kar/ F. Broeun/nger Gore/0n K. 6/030 BY Mgw- Jan. 26, F R HQGER ET AL I STRUCTURAL UNIT WITH X-SHAPED INSERTS Filed July 22, 1968 3 Sheets-Sheet 2 INVENTORS. Kar/F. firaeunfng er Gordon K. 6/0 0 51 1977' OR/VE K5 Jan; 26-, .1971 Kf UM U AL' 3,557,512

STRUCTURAL UNIT WITH X-SHAPED INSERTS 3 Sheets-Sheet S Filed July 22, 1968 INVENTORS. Ker/f? Braeun/nyer BY Gordon/6 6/0 0 fldwwzi'a HTTORNEKS United States Patent STRUCTURAL UNIT WITH X-SHAPED INSERTS Karl F. Braeuninger, Ferguson, Mo., and Gordon K.

Glaza, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed July 22, 1968, Ser. No. 746,565 Int. Cl. E04c 2/36 US. Cl. 52615 2 Claims ABSTRACT OF THE DISCLOSURE An improved integral structural unit having top and bottom surface members, spaced apart by longitudinally extending, web members forming hollow spaces defined by the top, bottom and adjacent web members; said spaces containing a multiplicity of spaced-apart strengthening rigid inserts. The improved unit may be detachably interlocked with other similar units to form a relatively flat structural surface particularly suitable for high impact uses such as temporary aircraft landing strips and aerial delivery platforms.

PRIOR ART Many flat, detachably interlocking structures are known which may be formed into floors, decks, boating docks or bridges, roadways or aircraft runways. One such type of structure has top and bottom surface members spaced apart by longitudinally extending, web members forming rectangular hollow spaces or channels when viewed in transverse cross-section. Heretofore, such structural units as just described, particularly when subjected to frequent high impact stresses, have failed due to the shear and bending stresses which exceed the capability of the webs to absorb such stresses without detrimental deformation 0r fatigue cracking. The stresses deflect or deform the rectangular channels into parallelograms. As the loading is repeated, the channels become repeatedly distorted, the webs less able to resist permanent deformation or fatigue cracking, and the unit finally fails.

It is an object of the present invention to provide an improved structural unit having a high resistance to deformation and deflection, and therefore having a longer useful life. This and other objects and advantages of the present invention will become apparent from a reading of the following detailed description.

THE INVENTION To achieve the objects of this invention, a basic structural unit is provided having top and bottom planar surfaces spaced apart by a plurality of longitudinally extending, perpendicular web members. The improvement provided by this invention is that of placing in the hollow spaces or channels defined by the top, bottom and adjacent web members spaced-apart rigid inserts whose structural strength and design configuration are such that they provide increased resistance to deflection and/or deformation under high stresses.

FIG. 1 is a fragmentary isometric view showing one embodiment of a structural unit in accordance with the present invention.

FIG. 2 is an isometric view of another pattern of rigid inserts within the structural unit.

FIG. 3 is a fragmentary sectional view of the structural unit as shown in FIG. 1.

FIG. 4 is a fragmentary sectional view of another embodiment of a structural unit in accordance with the present invention.

FIG. 5 is a fragmentary sectional view of a structural unit in accordance with the present invention showing a preferred type of rigid insert.

3,557,512 Patented Jan. 26, 1971 'ice FIG. 6 is an isometric view showing a particular embodiment of a landing mat plank in accordance with the present invention.

Referring to FIG. 1, there is shown a structural unit 5 indicated generally by the numeral 10, which has an 4 upper surface member 12, a lower base surface member 14 and plurality of longitudinal, perpendicular web stiffeners or members 16. The top, bottom and web members define hollow spaces or channels 18. In accordance with the present invention, these channels 18 contain spacedapart rigid inserts 20.

The rigid inserts 20 are of such configuration, structural strength and spacing in the channels so as to impart additional resistance to deformation of the structural unit when such a unit is subjected to frequent impact stresses. FIG. 1 and FIG. 2 show two examples by way of illustration only of possible spacing of the rigid inserts in the structural unit. Materials suitable for use as the rigid inserts include metals and alloys, wood and plastic.

The inserts 20 may be substantially solid pieces of material such as shown in FIG. 1, FIG. 2 and FIG. 3 or, preferably a structural frame work or open lattice network as shown in FIG. 4 and FIG. 5. This latter open configuration has the additional feature of minimizing the weight increase to the structural unit while at the same time imparting a substantial strengthening effect.

FIGS. 4 and 5 show a preferred rigid insert 20 configuration of a substantially X-shaped element, optionally having at least one side member 22 connecting the cross members; at least one of the cross members having on an open side an outwardly projecting arm 24 of such a size and length so as to elastically deflect when the insert is pressed into the channel. Once the insert is in place, arm 24 acts as a tension spring, i.e., self locks, to keep the insert in place. FIG. 5 shows two side members 22 for example only; the self locking insert is equally effective with none, one or three side members.

Alternatively, the inserts may be kept in place once in the structural unit by some adhesive material. Also the insert may be constructed of an expandable material, e.g. heat-expanding plastic, which expands to hold itself in place. In any event the inserts are such that they become as one with the basic structural unit.

The upper and lower surface members 12 and 14 respectively of the structure are preferably elongated rectangles but other shapes may be employed. Likewise, it is usually desirable, from the standpoint of light weight and high strength, for the structure 10 and rigid inserts 20 to be made of aluminum or its alloys, but other materials may be used. In general, any basic structure of this type is useful herein if it is substantially hollow or filled with passages.

The use of rigid inserts 20 in the hollow spaces of the structural unit provides the added strength and resistance against the deformation previously discussed to prevent structural failure of the unit. The structural unit of the present invention resists change in channel shape, i.e., parallelograming, caused by repeated impact stresses or shocks.

The following examples are representative of the present invention but are not limited thereto.

EXAMPLE I "FIG. 6 shows a specific type of structural unit, a landing mat plank, made in accordance with this invention. The overall thickness of the basic structural unit 10 is 1 to 4 inches, with the top 12 and bottom 14 surface members each being about inch thick. The thickness of the individual web members 16 is about inch thick, the web members being disposed generally perpendicular to the top and bottom surface members, spaced apart about 1% inches on centers and running lengthwise of the plank, thereby defining thirteen channels 18. The inserts 20 are of a configuration similar to that shown in FIG. 5, with cross members being about A; inch thick, side members 22 and locking arm 24 being about inch thick, and having a length of 75 to 200 percent the length of the longest cross sectional dimension of the channel, i.e., the height or the width. For purposes of illustration only the inserts are arranged in a lengthwise repeating 3252 pattern, spaced apart about 6 inches on centers. The planks are, as cut to length, about two feet wide and twelve feet long, and may be interlocked with other landing mat planks, e.g., by end connector elements 26.

EXAMPLE II Two samples of a structural unit of a construction similar to that above described, 6 inches long, 19 inches wide, having 13 channels defined by the top, bottom and web members, were subjected to a bending test. One sample unit which was Within the present invention contained rigid inserts made of an aluminum alloy and of a design similar to FIG. 5, 1 /2 inches in length, placed in each channel of the test unit. The other unit was used as a control and contained no inserts.

Various stresses were applied normal to the test and control unit surfaces. For each stress application the amount of deflection, a a measure of the strain on the unit, was noted. A graph was maintained plotting the stress applied against the deflection measured. An arbitrary failure point was selected at the stress at which the plot became appreciably non-linear.

The failure point for the unit without inserts was about 2,900 pounds stress. The failure point for the unit with inserts was about 7,800 pounds stress. Thus the improved unit of the present invention is able to withstand stresses without failure more than double that of the conventional non-insert unit.

Furthermore, after a final stress of about 4,300 pounds was applied to the non-insert unit, the measured permanent deflection was over inch from the horizontal. On the other hand, after a final stress of about 8,200 pounds, the permanent deflection of the unit with inserts was only /2 inch from the horizontal. Thus the improved unit of the present invention is capable of withstanding substantially higher stresses with significantly less permanent deformation than the conventional non-insert unit.

Various modifications can be made in the present invention without departing from the spirit or scope thereof for it is understood that the invention is limited only as defined in the appended claims.

What is claimed is:

1. A structural unit having top and bottom surface members spaced apart by longitudinally extended web members, said top and bottom members and said web members defining a plurality of channels when viewed in transverse cross-section; and throughout said channels a multiplicity of spaced apart, rigid inserts of a subtantially X-shaped configuration having two cross-diagonal members and an outwardly projecting arm on at least one of the cross members, the length of said arm being such that the arm elastically deflects when placing the insert in the channel and exerts pressure on the channel Wall when the insert is in place.

2. The unit of claim 1 wherein the insert has at least one side member connecting the ends of said cross-diagonal members.

References Cited UNITED STATES PATENTS 2,274,703 3/1942 John 52-615 2,333,600 11/1943 Trautvetter 526l5 2,392,552 1/1946 Roe 52-606 2,467,558 4/ 1949 Kapnek 52-695X 2,985,411 5/1961 Madden 52615X 3,331,177 7/1967 Godfrey 52615X 3,450,010 6/1969 Harvey 9413 FOREIGN PATENTS 145,901 1920 Great Britain 52-615 JOHN E. MURTAGH, Primary Examiner US. 'Cl. X.R. 1085 1 

